Manufacture of glass-filled screw plug bases



March 8, 1932. L. BRUZZONE MANUFACTURE OF GLASS FILLED SCREW PLUG BASES Filed Aug. 30, 1928 Patented Mar. 8, 1932 j UNITED STATES PATENT omcz Ii UIGI BEUZZONE, OI GENOA, ITALY, ASSIGNOB TO mama ABCHIKEDE BANDINI,

OI GU05, ITALY murac'ruan or amass-numb scanw 2mm mans Application filed August 80, 1928, Serta1 No. 308,078, and in Germany July 28, 192%.

. This invention relates to a method of fOlIIl-r ing a perfectly homogenous glass core in a metallic shell and is especially directed to improvement of the uality or grade of spark plugs especially for internal combustion engines.

One of the objects of the invention is to manufacture a spark plug having a transparent' core and which will withstand high temperatures and pressures such as exist in the cylinders of internal combustion engines.

With this and other ends in view, the invention is directed to the formation-of a perfectly homogenous and compact glass core indissolubly adhering to the metallic screw base of the plug and carrying centrally a metallic electrode, the whole forming a perfectly gas-tight indissoluble unit.

In order to withstand high temperatures and to aid in burning the oil particles projected into the bottom cavity of the plug, the invention provides also the mounting, upon a shoulder formed inwardly of the shell, of a flanged sleeve made of porcelain or like refractory matter, on which the glass is applied in a soft condition and pressed, so that its flange remains embedded between the shell shoulder and the glass core, and with its sleeve portion projecting parallel to the walls of the lower plug cavity and slightly apart therefrom.

The invention also consists in an improved method of manufacture of spark plugs of this kind by softening by heat and compressing into the plug base thus prepared the glass core with its central electrode positioned therein and the flanged porcelain sleeve, the whole so as to insure a gas tight fit and to exude through radial holes by compression all the gas bubbles in the glass and the glass material in excess of the displacement of the pressure plunger.

In the drawings:

Figure 1 is a sectional elevation of a plug, the base portion of which is manufactured according to the invention;

Figure 2 is an outside elevation of the plug shown in Fig. 1; and Figure 3 is an axial sectional view showing the step of the manufacture of the plug in which the glassy mass is subjected to pressure.

The manufacture of the plug according to the invention takes place as follows In the plug casing 1 is inserted the porcelain sleeve 7 as shown in Figures 1 and 3 and then there is inserted the fusible glass, such as pyrex glass, preferably in the shape of a tubular piece having an outer diameter slightly less than that of the plug casing, whilst the inner diameter of the tubular piece is slightly larger than that of the conductor 3. Theplug casing thus prepared is now laced in a furnace and heated up to a lig t red glowing heat. At the same time the metal conductor 3 is heated in a furnace up to a dark red glowing heat. The conductor 3 forthis purposeis inserted in a support 13 which is applied on a handle 14. The support 13 with the conductor heated up to dark red is now placed with the handle 14 in a press device and afterwards there is applied upon the upright fastened conductor from the top, the glowing casing 1 until the lower edge of it is in correspondence with the upper edge of the handle 14. Afterwards the movable hot piston 15 of the press device Figure 3 is put into motion so that it exerts a uniform pressure upon the pasty mass, whereby an intimate connection of this glass mass is created with the plug casing and the conductor.

In order not to expose the plug casing during the compression to excessive strains which might deform it, it is formed with the radial holes 12 through which the glass material in excess can exude towards the exterior. These holes ofier in this way safety means preventing the deformation of the plug casing; these holes besides offer the advantage that no particular attention has to be given to the pressure employed and even inadmissible elevated pressure may be adopted without damaging the plug casing. These holes also allow the escape of air from the interior of the plug casing.

After the cooling down of the plug the same is now supplied with the accessories, that is, with the electrodes 6, the glass body 8 by inserting the packing 11 and the mica tube 9, after whichthepartswillbetightened to ther by the double nut 10.

avin now particularly described and ascertainef the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. A method of manufacture of ark plugs comprising a short metallic shell avmg radial apertures, comprlsing the step of introducing the insulatin material of the core into the metallic shel heatin the shell to glowing red, separately heating t e central electrode fastened to a base piece to dark red, transferring then this base piece with the electrode on to a plunger press having an axially perforated pressure plunger or die, inserting upon this electrode and base the glowing glass-filled shell and subjecting the glass within the plug shell to the compression of the previously heated pressure plunger of the press for a predetermined stroke of the plunger, the excess glass and gas bubbles being thus extruded from the'shell through the radial apertures.

2. A method of manufacture of spark plugs having a short metallic base sleeve or shell supplied with an inner shoulder and radial holes, comprising the step of introducing into the shell a flanged refractory sleeve with the flange resting upon the shoulder, introducing the insulating material of the core into the metallic shell, heating the shell to glowing red, separately heating the central electrode fastened to a base piece with the electrode on to a plunger press having an axially perforated pressure plunger or die, inserting upon this electrode and base the glowing glass-filled shell and subjecting the glass within the plug shell to the compression of the previously heated pressure plunger of the press for a predetermined stroke of the plunger, the excess lass and gas bubbles being thus extrudeg from the shell through the radial apertures.

In testimony whereof I have signed my name to this specification.

LUIGI BRUZZONE.

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